1. Field of the Invention
This invention relates in general to the construction of delivery systems for dispensing precise quantities of material and in particular to a new and useful dosing system for feeding powdery or granular material which is delivered through a separate coarse dosing conduit and subsequently through a fine dosing conduit.
2. Description of the Prior Art
There are many known dosing devices in which the material flow is fed from a delivery line by switching it into a secondary line which is branched off from the main line and which is opened up into a weighing receptacle. At a certain switch off point the flow is switched back and the further material in the delivery line is fed back into a receiving bunker through a ring shaped conduit portion. In addition similar devices are known in which two switch off points are provided and the entire material flow is first directed in the manner of a coarse dosing into the weighing receptacle and upon reaching the first switch off point the device is switched over to an intermediate position in which a fine dosing takes place. As soon as the second switch off point is reached a further feeding of the material into the weighing receptacle is completely stopped and a ring shaped conduit portion connected back again to the receiving bunker. These known dosing devices are suitable on condition that, the delivery of the material is accomplished by means which insure a uniform feeding free from thrust and in particular is applicable for delivering fluid or air suspended material. In addition the material still present in the line at the moment of the switching off must always be reconveyed into a silo or a receiving bunker. Thus in the pneumatic systems in which the material is passed into a weighing receptacle in the form of individual plugs, the devices which are known cannot be used because the kinetic energy of the incoming plug would lead to an incorrect weighing. In mechanical balances, the momentum of the material plug causes an oscillation of the balance and also produces an incorrect weighing. Thus it is not sufficient to close the valve in the delivery line and obtain the desired weight because the balance can oscillate both toward the short weight and toward an overweight.